Pressure crystallization equipment

ABSTRACT

Pressure crystallization equipment which effects segregation by the use of pressure as a variable, particularly characterized in that after crystallization has occurred, the separation of a solid from the mother liquid is safely effected irrespective of the high pressure by providing a filter structure made of a cylindrical metal mesh layer structure and a cylindrical reinforcing member backing it up.

FIELD OF THE INVENTION

The present invention relates to pressure crystallization equipment forcausing a liquid to become solid at high pressures, such as 500 atms ormore, and more particularly to equipment for use in solidifying a liquidcontent under such high pressures and separating it in the form of asolid from the mother liquid mixture.

BACKGROUND OF THE INVENTION

When two or more substances are present in a liquid state or in a slurrystate (hereinafter referred to as the liquid mixture), there have beenmany chemical methods for separating a particular content from the othercontents. However, the conventional methods are not effective toseparate one particular content from others when the contents areeutectic or form a solid solution, where the contents are so similar inchemical and physical properties that they are difficult to separate. Asa result the common practice is to effect the separation of contents atparticular temperatures, which will be referred to as coolingcrystallization. This includes a cooling method under which a particularcontent is separated at its freezing point from the others.

However cooling crystallization has some disadvantages; for example, (1)it is difficult to control the temperature, (2) temperature gradientsare likely to occur in the system, thereby preventing the achievement ofthermal equilibrium and (3) the operational time is prolonged.

Therefore the inventors have started to solve the problems encounteredin cooling crystallization and have developed a crystallization processutilizing pressure instead of heat, hereinafter referred to as pressurecrystallization equipment.

As the pressure crystallization method is operated for commercialpurposes, particularly using large-scale equipment, new problems havearisen. One of them is how to discharge the liquid phase out of thesystem under a high pressure when the liquid and solid phases co-existas a mixture therein.

Under the pressure crystallization method with the rise in pressure thecrystallization proceeds, whereas as the pressure is decreased thecrystals melt or become soft. As equipment a cylindrical highpressurevessel is used, which is provided with a filter on its inside wall.Behind the filter the system is communicated with the atmosphere whereinthe communication is blocked by means of a valve when it is intended toallow liquid and solid phases to co-exist. There are many modificationsto it.

In operation a mixture in a liquid state is put in the vessel; thecommunication with the atmosphere is blocked and the discharge of aliquid is closed, which means that the vessel is completely closed. Ahigh pressure is applied to the mixture in the vessel; if necessary, thetemperature is reduced. In this way the particular content iscrystallized in the mixture, thereby producing a state in which theparticular fraction of crystals and the remaining liquid co-exist. Thenthe valve is opened so as to withdraw the liquid content, which isforced out through the filter by applying pressure to the mixture in thevessel. The pressure is continuously applied to the remaining solidphase so as to squeeze it and force the remaining liquid through thefilter. In this way a highly pure content remains in the vessel.

Reference will be made to FIG. 1, which shows an example of aconventional high-pressure vessel. The vessel 1 has as filter 2, athermal insulating material 3, a piston 4, a bottom closure 5, a mixturesupply pipe 6, and a discharge pipe 7.

The steps taken to operate the illustrated vessel are as follows:

(1) A valve V7 is closed and the valve V6 is opened so as to allow themixture to enter the vessel 1;

(2) After the supply of mixture is completed the valve V6 is closed, andthe piston 4 is caused to descend, thereby causing an increased pressureupon the mixture in the vessel. In this way the crystallization of aparticular content is promoted;

(3) After the crystallization is finished the valve V7 is opened and thesubsequent filtering and squeezing start; that is, first, the liquidcontent in the vessel is squeezed, and caused to pass through thefilter. The fluid content passes through a path 8, and is dischargedthrough the pipe 7 via the valve V7; and

(4) After the filtering and squeezing are finished, the vessel 1 isopened, the solid cake at the atmospheric pressure is taken out oralternatively, is melting for recovery.

In the process (3) mentioned above the filter 2 is subjected to as highpressures as 500 atms or more, sometimes a few thousands atms, in thedirection of arrow (A), that is, perpendicular to the filter surface. Inaddition, as the squeezing advances, the filter surface is subjected toa frictional force involved in squeezing the solid cake wherein thefrictional force acts on the filter surface in the dirction of arrow(B), that is, in the axial direction. Furthermore, a differentialpressure between the high internal pressure acting on the upper ring 2aand a possible atmospheric pressure thereunder affects the filtersurface. Owing to these combined factors the filter is in danger ofcompressible deformation in the direction of arrow (B), and sometimes indanger of expanding deformation in the direction of arrow (A);sometimes, the filter breaks owing to the expanding deformation. Whenthe filter is made of a sintered metal (SUS or the like) having a simplestructure it often happens that the pores in the filter are crushed andclogged, thereby losing the filtering ability.

As described above the conventional pressure segregation method has agreat disadvantage of filter fracture and/or lost filtering ability.This leads to a reduced efficiency in the form of low yields or thereduced purity of a collected content.

In order to solve these problems occurring in the process of filteringand squeezing it is essential to develop a cylindrical filterstrengthened radially as well as axially.

In order to overcome the difficulty mentioned above the inventors havemade an invention for which a patent application No. 59(1984)-50108 hasbeen filed. In this invention the upper portion of the inside wall ofthe filter is fixed to the ring, and the filter is backed up by areinforcement and fixed at a given place in the vessel so as to protectthe filter against axial deformation.

As is shown in FIG. 2 the entire structure is substantially the same asthe embodiment of FIG. 1. A ring 9 is fitted in a space above the filter2 and a cylindrical reinforcement 10 is provided behind the filter 2through a thermal insulating material 2. The reinforcement 10 is soconstructed that its length can be adjusted in accordance with the axiallength of the filter so as to locate the upper ring 9 at a desiredposition. The reinforcement 10 can be cylindrical when the insulatingmaterial 3 is interposed against the filter 2 or vertically split forfacility of attachment and detachment. The insulating material 3 has astructure which permits the liquid to pass therethrough toward thedischarge path 8. When no insulating material 3 is interposed, it isnecessary to provide a vertical slit whereby the liquid is permitted toflow after having passed through the filter 2.

The size of the slit must be determined so as to reinforce the filterstructure in the axial and radial directions. It is possible to make thering 9 in one body with the reinforcement 10.

In this way the filter 2 is fixed at a particular place with the ring 9and reinforcement 10, and if it is additionally backed up by thereinforcement 10 the filter 2 is protected against deformation in thedirections of arrows (A) and (B) and against its pores being crushed orexpanded. Thus the high yield and the purity of a collected componentare ensured. Because the filter 2 is protected against becoming damagedthe frequency of replacing the filter with a new one is considerablyreduced.

FIG. 3 shows another embodiment of the previous invention, which ischaracterized in that the filter 2 is fixed at its upper and lower endsby means of rings 9 with the reinforcement 10 interposed therebetween.Owing to the rings provided at both ends the filter 2 is safelyprotected against compressive and expanding deformation.

FIG. 4 shows a further example of the embodiment. In this example thecylindrical filter 2 has a progressively divergent wall, that is, atapered wall. The reinforcement 10 and the insulating material 3 areequally shaped, and they are provided between the upper and lower rings9, with a spacer 11 being provided in the outermost layer. The spacer 11is cotter-shaped in cross-section as shown in FIG. 4.

In order to prevent the filter from becoming deformed along itscircumference it is necessary to minimize the space between theinsulating material 3 and the reinforcement 10 located behind the filter2. In the examples shown in FIGS. 1, 2 and 3 where the filter 2 ispurely cylindrical, the minimized space is almost impossible when thefacility of inserting the filter is taken into consideration. Theembodiment shown in FIG. 4 has solved this difficulty. Spacer 11functions as a wedge, thereby placing the reinforcement 10 into tightcontact with the back of the filter 2 to the extent that no space isproduced therebetween. In addition the filter is prevented from becomingdeformed in a radial direction. When the filter 2 is to be removed theblock 5 has only to be pushed downward. In the process of squeezing, thefilter 2 is subjected to a downward frictional force. As shown in FIG. 5(the straight line shows a pre-squeezing state and the broken line showsan under-squeezing state) the solid cake is subjected to a force wherebyit is urged to separate from the inner surface of the filter 2, whichmeans that the friction lessens. The solid cake is squeezed when it isin the state shown by the broken line in FIG. 5 as it is subjected to aseries of buckling fractures during which a liquid path is producedinside the cake, thereby facilitating the separation of liquid andsolid.

In the embodiments mentioned above the filter is made of sintered metalmesh, but the material is not limited thereto: mono- or multi-layermetal mesh, a porous plate, a laminated sintered material, a piece ofcanvas or their combination can be selected in accordance with thepressure and the nature of the treating material.

The results of the research conducted prior to the present inventionhave been described as the background of the present invention. Thecontents of the research has not yet been published and is not availableto the public. Under the new pressure crystallization method the filtersometimes has fractured and a clogging trouble has occurred. There hasbeen a strong demand for an improved pressure segregation method andequipment.

The next problem is how to control the temperatures during theoperation.

The pressure segregation method uses pressures as a variable, but heatis unavoidably generated and it is necessary to control the temperaturesso as to minimize the influence of heat. In order to carry out thepressure crystallization method efficiently it is essential to controlthe temperatures likely to rise in the course of operation. One solutionis to place the mixture kept at lower temperatures in the vessel.However in the processes (2) and (3) heat is likely to generate and thetemperature in the vessel instantaneously rises by 10 degrees or more.The wall of the vessel has such a large heat capacity that the heatgenerated is absorbed in the wall, thereby restraining a further rise inthe temperature. As the heat radiates, the temperature lowers. As aresult there arises temperature gradient in the vessel, which results inuneven segregation. In such situations the collecting liquid content islikely to crystallize in large quantity on and around the filter and/orin the discharge path, thereby preventing the smooth separation ofliquid and solid contents. There is another solution, that is, thepressure in the vessel is slightly reduced so as to melt the crystals oflower purity, and enhance the purity of the collected solid content.When the pressure is reduced in this way the treated substances tend tohave lower temperatures than the filter and the inside wall of thevessel, which may lead to the excessive melt of solid phase to changeit.

The temperature gradient is an important problem in that (1) it islikely to impair the purity of a collecting content because of apossible crystallization of other than the desired content, (2) thedischarge path is likely to become clogged, thereby reducing theperformance of the filter, and (3) the crystals of the particularcontent are likely to melt, thereby resulting in a reduced yield.

The above-mentioned problems are amplified by daily and seasonal changesin temperature which affect the temperature of the vessel, therebyrequiring a strict control of the temperatures of the vessel.

However the control of temperature is very complicated, and is a labor-and money-consuming work. In addition the vessel unavoidably has a largeheat capacity because of its construction of thick metal. This makes thecontrol of temperature difficult. One solution is that the vessel isconstructed such that heat transfer between the wall of the vessel andthe inside thereof is minimized. The embodiments shown in FIGS. 1 to 4have achieved this solution to some extent.

Another difficulty is how to take out solid cakes remaining in thevessel after the filtering and squeezing have been finished. When thevessel is purely cylindrical having an equal diameter along its entirelength, a high pressure such as 500 atms or more than 1,000 atms acts onthe inside of the filter. Such a high pressure can break not only theinside of the filter but also expand the wall of the vessel. Under thissituation the particular content to be collected is tightly packed in asolid cake in the vessel after the squeezing has been finished. At thisstage the piston is raised so as to release the high pressure andrestore a normal atmospheric pressure in the vessel. Then the piston isagain lowered, or the vessel is lifted up against the piston, so as topush the solid cake. However when the pressure is reduced to the normalpressure as mentioned above, the wall of the vessel tends to restore itsoriginal capacity. As a result the solid cake is tightened along itscircumference, thereby placing it into tight contact with the insidesurface of the filter. In this situation if the solid cake is toostrongly pushed by the piston toward the bottom of the vessel a largefriction acts in between the solid cake and the filter, thereby damagingthe inside surface of the filter. Thus the life of the filter isshortened. Frequent replacement will be necessary. To solve this problemone way is to use a thick filter, which, however, leads to a high cost.In this respect the embodiment of FIG. 4 has been found effective.

There is a further problem encountered in the separation of a liquidcontent from the liquid/solid mixture:

The liquid content is kept at a high pressure, and when it is dischargedto a low-pressure side through the filter and the discharge pipe, therearise a sudden drop in pressure, which transfers to the solid phase inthe vessel. As a result the solid phase begins to melt, thereby reducingthe working efficiency. Therefore it is necessary to keep the highpressure in the vessel as extensive as possible. One basic idea is toprovide a pressure buffering chamber such as a hatch. On the basic ofthis idea there are (1) a method of using a pump connected to thehigh-pressure side, whereby the high-pressure liquid is pumped as it isat the high pressure from the solid phase, and then it is withdrawn tothe low-pressure side, or alternatively, (2) a method of placing aanti-pressure device of the same type and size as the pressuresegregation equipment at a place adjacent thereto. As evident from thedescription these methods are disadvantageous in being costly andcomplicated.

At any rate it is difficult to take out a high-pressure liquid contentto a low-pressure side while the liquid is being kept at the highpressure, and it is essential to develop an equipment achieving thisdifficult task.

In association with the above-mentioned difficulty there is a problem ofclogging in the discharge path owing to the high-pressure-unavoidablyacting on the discharge path thereby to produce crystals under theinfluence of the pressure. When the clogging occurs in the dischargepath is is necessary to melt and remove the crystals by an extra step.This is also a time- and labor-consuming work. The regular course fromsupply of material to discharge of the product takes a few minutes, andin normal operation the process is continously repeated day and night.If the discharge path clogs, the regular course of operation is broken.The working efficiency is considerably reduced. In order to solve thisproblem one solution is to heat the entire equipment at a certaintemperature. This requires a lot of heat energy, which reflects in thehigh production cost. In addition if heat is added to the totalequipment it must be covered with an insulating material so as to keepthe heat, thereby making it difficult to observe from the outside. Forexample it is difficult to inspect a liquid leak in the couplings orjoints in the equipment.

As has been so far pointed out the conventional pressure crystallizationmethod and equipment have many problems arising after thecrystallization has taken place, and the present invention aims atsolving them and increasing the efficiency of separating a particularcontent from the remaining liquid mixture.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved pressurecrystallization equipment which is free from filter fracture andclogging likely to occur owing to the high pressure given in thesqueezing process.

Another object of the present invention is to provide improved pressurecrystallization equipment in which heat transfer is minimized betweenthe wall of the vessel and the inside thereof.

A further object of the present invention is to provide improvedpressure crystallization equipment which allows the solid cake to bereadily removed from the remaining mixture without damaging the filter.

A still further object of the present invention is to provide improvedpressure crystallization equipment which discharges a liquid contentfrom a high pressure side to a low-pressure side.

Other objects and advantages of the present invention will become moreapparent from the following description when taken in conjuntion withthe accompanying drawings which shows, for the purpose of illustrationonly, one embodiment in accordance with the present invention.

According to one aspect of the invention there is provided pressurecrystallization equipment which comprises:

a cylindrical high pressure vessel having an inner surface;

means for establishing a pressure of at least 500 atmospheres withinsaid vessel; and

a filter structure disposed within said vessel and being fixed againstsubstantial radial and axial displacement with respect to said vessel,said filter structure comprising a cylindrical metal mesh structurehaving at least two layers of mesh sintered together and a reinforcementdisposed between said cylindrical metal mesh structure and said innersurface of said vessel for backing up said cylindrical metal meshstructure, said reinforcement and said cylindrical metal mesh structurebeing joined together at least at opposite ends thereof, there being atleast one liquid flow path through said reinforcement, wherein adifferential pressure between an inside and an outside of said filterstructure is maintained by the inner surface of said vessel.

According to another aspect of the present invention there is a providedpressure crystallization equipment mentioned above, wherein the filterstructure and the vessel have a thermal insulating layer interposedtherebetween, or wherein the inner surface of the filter structure isshaped like a truncated cone divergent toward the open end of thevessel, or wherein the vessel is communicated with a nozzle arrangementin the discharge path, the nozzle arrangement comprising a nozzle havinga smaller diameter than that of the discharge path, or wherein thedischarge path has an insulation-clad heater.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a vertical cross-section through pressure crystallizationequipment made by the inventors of the present application;

FIG. 2 is a vertical cross-section showing the filter structure shown inFIG. 1;

FIGS. 3 and 4 each are modified versions of the pressure crystallizationequipment of FIG. 1, each corresponding to FIG. 2;

FIG. 5 is an explanatory view exemplifying the process of squeezingoperated under the equipment of FIG. 4;

FIG. 6 is a horizontal cross-section showing a filter structure used inthe pressure crystallization equipment;

FIG. 7 is a horizontal cross-section showing the filter structure usedin the pressure crystallization equipment of the present invention;

FIG. 8 is a vertical cross-section through pressure crystallizationequipment embodying the present invention;

FIG. 9 is a vertical cross-section showing an embodiment including aninsulating layer;

FIG. 10 is an explanatory view exemplifying a discharge path including anozzle arrangement;

FIG. 11 is a cross-section on a larger scale of the nozzle arrangementof FIG. 10;

FIG. 12 is a vertical cross-section showing an embodiment including aheating element in the discharge path ; and

FIG. 13 is a vertical cross-section showing an embodiment including aheating element in the pressure gauge.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 6 the pressure crystallization equipment of thepresent invention includes a cylindrical metal mesh layer structure 12,and a cylindrical reinforcement 13 provided concentrically of the meshlayer structure 12 so as to back it up. The two members 12 and 13 arejoined to each other at least at their opposite ends, and preferably asolid phase diffusion joint layer is interfacially providedtherebetween, and the two members 12 and 13 will be referred to jointlyas the filter structure 14. The filter structure 14 is fixed axially andradially on the wall of a vessel 1. The filter structure 14 can be fixedin a known manner; for example, by means of rings 9 shown in FIGS. 3 and4. In the radial direction the filter structure 14 is kept in contactwith the inside surface of the vessel 1 with a minimum gap such as 0.1mm or less.

The filter structure 14 is intended to allow a liquid to pass frominside to outside, and the liquid is collected at the bottom of thevessel 1 for discharge out of the equipment. A more detailed descriptionwill be given below:

The filter structure 14 includes two or more cylinders of metal mesharranged concentrically, prefereably each cylinder having different meshsize from the other's; for example, the inner cylinder having a finemesh whereas the outer one having a course mesh, and when threecylinders are used, the middle one has a finer mesh. The cylinders arefirmly fixed to each other so as to withstand a stress axially actingthereon, thereby avoiding a possible interfacial displacement. Howeverit is necessary to allow gaps to exist in between the adjacent meshcylinders in that the gaps are necessary to allow the liquid to passthrough, wherein the gaps are produced owing to the wavy forms of theindividual wires constituting the metal mesh. Usually the metal meshcylinders are joined to each other by sintering, and the sinteringconditions, such as sintering pressure and temperature, are determinedin accordance with the diameter of the constituent wires, the mesh size,and the nature of the material.

The reinforcement 13 is designed to support the metal mesh cylinder sothat the cylinder 12 is protected against an axial and radial forceacting thereon. The reinforcement 13 is made by machining a metal blockand further is provided by machining a path allowing a liquid to passthrough, the path leading from inside to outisde and communicating witha discharge pipe. It is preferred that the diameter of the reinforcementis such as to allow a small gap to be present against the outsidesurface of the vessel.

As described above it is essential to join the metal mesh layerstructure 12 and the reinforcement 13 is firmly as to withstand an axialforce and a radial force acting thereon, and in order to secure thejoint they can be soldered to each other in place along the lengthsthereof. Thus they are protected against a possible fructure ordisplacement. Solid phase diffusion bonding can be preferred, which canbe effected by sintering. The diffusion sometimes spreads to cover theliquid paths mentioned above, and to avoid it grooves 15 are formedaxially or circumferentially. The grooves can guide the liquid frominside the structure 12 into second grooves 16 by way of by-passes 15a.Finally the liquid can be discharged in the same manner as mentionedabove with reference to FIG. 1. In the illustrated embodiment thegrooves 15 and 16 are produced in the reinforcement 13.

It is important to locate the two members 12 and 13 exactly with respectto the vessel 1. The small gap between the reinforcement 13 and thevessel 1 is helpful to maintain them in the radial direction. In theaxial direction a spacer (not shown) can be provided to that the innerheights of the vessel 1 and the reinforcement 13 are made equal. Ifeither member is dislocated with respect to the other they are liable toradial or axial stress possibly acting thereon owing to the highpressure, thereby damaging the equipment and/or endangering the operatorengaged in operating the equipment.

The exact location of the filter structure 14 is important in that thespace defined by the filter structure must be concentric of the axis ofthe piston. Another consideration is that the filter structure tends toexpand radially during filtration and squeezing under the high pressureor a high pressure differential. To avoid the radial expansion thefilter structure 14 is placed in contact with the inside of the vessel 1with the minimum space interposed therebetween so as to stop the filterfrom expanding outside. When the liquid phase is withdrawn the filter 14contracts thereby to squeeze the solid cake. But under the structure ofthe present invention this problem is avoided or minimized. For thispurpose the space between the filter structure and the vessel ispreferably 0.1 mm or less. The embodiment shown in FIG. 4 is effectiveto achieve this purpose, that is, the filter structure 14 is taperedwith a cotter-like spacer interposed between the filter and the vesselso as to tighten the filter structure or alternatively the vessel istapered whereas the outside of the filter is shaped like a truncatedcone, so that the vessel and filter are arranged concentrically so as tobe complemental with each other. Either can be adopted.

FIG. 8 shows an example of the equipment for achieving the abovementioned purpose. The vessel 1 is provided with a spacer 11 having atapered wall, and a filter structure 14 having an equally tapered wallso that the filter structure 14 is exactly and firmly located withrespect to the vessel 1.

In the embodiment shown in FIG. 8 the blocks 5 and 5a are detachable,which facilitates the supply of the filter structure and the removal ofthe contents from the vessel.

FIG. 7 is a rough view showing the structure of the filter structure 14,wherein the reference numerals 12a to 12e denote metal mesh bodies allof them constituting the unitary layers structure 12, which issurrounded with the reinforcement 13. Functionally the layer 12b of thefinest mesh size plays as a filter whereas the others work as supportsfor the layer 12b and provided routes for allowing the liquid to passthrough.

Referring to FIG. 9 another example of the preferred embodiments will bedescribed:

There is provided a thermal insulating partition 17 between the vessel 1and the filter structure 14, thereby preventing heat from transferringto the vessel 1, wherein the heat is likely to be generated at theinside of the filter structure 14. In the illustrated embodiment thefilter structure 14 is provided in a lower section of the cylinder butit can be provided along the entire height thereof. When the filterstructure 14 is provided in the lower section thereof as shown in FIG.9, there is provided an insulating spacer 19 between the vessel 1 and ahigh pressure chamber 18, thereby protecting the collecting productagainst heat. In addition the filter structure 14 is firmly fixed inposition. The reference numerals 20 and 21 denote insulating membersadapted to prevent heat from transferring to the main section of theequipment; preferably they are provided with filter members 20a and 21a,respectively. A plug 5a is made in one piece with the vessel 1, andother parts are detachably fixed to their positions so as to allow thesolid cake to be readily taken out.

Under the present invention the vessel is insulated against heat fromthe products in the cylinder, and particularly the transfer of heat inall directions from the filter structure 14 is prevented. This reducesthe heat capacity of the filter structure 14. This is effective to avoidthe production of temperature gradient between the inner surface of thefilter structure and the central portion thereof. As a result the solidcake is kept at a constant temperature throughout it. This leads to thehigh purity of the products. Under the conventional practice with thedecrease in the temperature of the product sticking to the inner surfaceof the filter, other content than the desired one crystallizes andresults in (1) the reduced purity of the product and (2) the lostfiltering ability die to clogging troubles in the inner surface of thefilter. Under the present invention these problems have been avoided orminimized.

For the insulating material bakelite or epoxy resins can be selectivelyused but there is no limitation to the material if it has someelasticity, has a compresible strength and has a chemical resistivity tothe treating content. The insulating material is variously shaped inaccordance with the position at which it is located. Basically it isshaped so as to allow the liquid to pass therethrough and flow downwardtoward the bottom of the equipment. The thickness of the insulatingmaterial is determined in accordance with the operational condition.Alternatively it is possible to cover the reinforcement with aninsulating film. (Of course, whenever thermal insulation is not needed,partition 17 may be made of metal.)

Next, the method of drawing the liquid from the vessel to a point whereit is under the atmospheric pressure through the filter structure withthe use of a nozzle will be described:

The liquid from the discharge pipe is immediately exposed to a lowpressure, but upstream of the nozzle a high pressure is maintained.Therefore the filtering operation can be finished while the solid phasecan be kept at the high pressure. This is one advantage derived from theuse of a divergent nozzle. In general when a squeezing force is appliedto a solid and liquid coexisting phase so as to force out the motherliquid through the filter structure, a greater part of the mother liquidis caused to pass through the filter structure at the initial state ofthe squeezing process because of having no obstacle on and around thesurface of the filter structure 14. As the squeezing advances,crystallized solids gather thereon, thereby increasing the resistance tothe filtering. Toward the end of the squeezing process the amount of thefiltrate considerably lessens. In this way the amount of filtrate isreduced with time, which means that the amount of the liquid passingthrough the nozzle is gradually reduced. In the process of squeezing andfiltering the high pressure chamber is full of crystallized solids,which gather on the surface of the filter structure and prevent themother liquid from discharging therefrom. As a result the fresh solidcake is not pure enough.

The inventors have devised to control the high pressure in the processof squeezing and filtering so as to allow the mother liquid to passthrough the filter as much as possible. Under this device the amount ofthe high pressure liquid continues to lessen, and the discharge pressureequally continues to reduce from the start of squeezing up tothe endthereof in irregular patterns.

Because of the complicated changes in resistivity of the high pressureliquid prior to filtering it is essential to control such varyingresistances so as to achieve the desired results. One solution is toprovide a control valve in the discharge line, whereby the resistance ofliquid flow is controlled with time and pressure. However this methodhas disadvantages; for example, (1) the control of flow rate must becarried out in a short time, (2) the follow-up troubles due to changesin the liquid pressure and (3) the troubles proper to the valve.

In order to overcome the problems pointed out above the inventors havedevised to use a divergent nozzle whereby the resistance or the rate offlow is controlled. The diameter of the nozzle is an important factorwhich affects the control of the flow rate. If it is too large the flowrate naturally becomes too large, thereby causing the crystallized finecrystals to flow out, and also leading to the reduced pressure in thevessel (which means that the pressure for driving the piston becomesinsufficient). To avoid the reduction of pressure it is required to usea great power. Whereas, if the diameter is too small the flow ratebecomes too small, thereby prolonging the operation time for squeezingand filtering. It is important to determine an optimum diameter of thenozzle so as to be in accord with the progress of squeezing andfiltering operation, which is evident from the following equation:

    V=a√2gH

wherein:

V: the rate of flow ejecting through the nozzle under pressure

a: coefficient

g: gravitational acceleration

H: the pressure of the liquid being discharged, expressed in terms ofwater head

It will be understood from the above equation that it is required toreplace one nozzle with another in accordance with the rate of flow tobe desired. In this case the maximum diameter depends on the capacity ofthe equipment to produce pressure, and more specifically, the hydraulicpower must be such as to compensate for the deficiency in pressure dueto the flow-out of liquid. The diameter D of the nozzle is expressed bythe following equation: ##EQU1## wherein: W: the driving energy of thehydraulic pump

P: pressure

ΔV: the amount of flow-out liquid per unit time

V: the rate of flow

By replacing one nozzle with another in accordance with the rate of flowto be desired the speed at which the separation is effected is adjusted.However it is troublesome to replace the nozzles frequently and duringreplacement the liquid is allowed to flow out, thereby resulting in thewaste in liquid.

The inventors have provided an arrangement of a plurality of dischargepipes 17 as shown in FIG. 10 in which three paths 17a, 17b, and 17c areprovided each including nozzles 23a, 23b and 23c having differentdiameters, respectively. The reference numerals 24a, 24b and 24c denoteelecromagnetic valves whereby the discharge path is automaticallyselected. The nozzle is selected by selecting the valve 24a, 24b or 24cin accordance with the flow rate to be desired. There are providedthrottle values 25a, 25b and 25c upstream of the nozzles 23a 23b and 23c(if so desired, downstream thereof), which work in cocoperation with therespective nozzles 23a, 23b and 23c. The reference numerals 26a, 26b and26c denotes filters, whereby the nozzles are protected against clogging.The liquid ejected through the nozzle has a large kinetic energy, and itis necessary to attenuate the kinetic energy as soon as possible so asto secure operational safety.

FIG. 11 shows an embodiment which includes ducts 31 provided downstreamof the nozzles, the ducts having a relatively large diameter withrespect to that of each nozzle. The duct is designed to absorb thekinetic energy by friction between the flow of liquid and the insidewall of the duct, whereby reducing the rate of flow to a safe speed.

Under the present invention it is possible to add any other auxiliarydevice to the arrangement shown in FIG. 10, and also to change thelengths of the ducts within the spirit of the invention. The diameter ofthe nozzle tends to enlarge by wear over a long period of use.Replacement is required but as the nozzle is a small component part theprice is low and the replacing work is easy. Without the use of alarge-scale equipment with withdrawal of the high pressure liquid to thelow pressure section is achieved in an optimum situation.

FIG. 12 shows an embodiment which incorporates a heating device locatedin the discharge path, which will be described in detail:

The reference character H denotes a heater of sheath type located in thedischarge paths 7 and 8 along the full length thereof. The heater H isinserted into the pipes 7 and 8 from a three-way coupling 27, whereinthe terminating end of the heater H is electrically connected to thesource of electricity directly or indirectly, that is, through the block5. The other terminating end of the heater H is soldered to thethree-way coupling 27, and a lead line is provided for connection to thesource of electricity. The coupling 27 is also connected to the valve V7(FIG. 1). A current constantly flows through the heater H, therebykeeping the paths 7 and 8 warm. This is effective to prevent the liquidflowing therethrough from solidifying, thereby avoiding a cloggingtrouble. Likewise a heater can be provided in the supply path 6, therebypreventing the supplying liquid from solidfying. A pressure gauge can beprovided in the section where no clogging is wanted, whereby the riseand drop in pressure is visually watched. A pressure gauge itself isessential to the equipment of the present invention but a high pressureacts within the pressure gauge, thereby causing the liquid flowingtherethrough to solidify. When the liquid solidifies in the pressuregauge it becomes difficult to obtain an accurate information about thepressure. The present invention has solved this problem. Referring toFIG. 13 to solution will be described in detail:

The reference numeral 28 denotes a pressure gauge unit which includes aheater of sheath type fixed by a fixing member 29, and the referencenumeral 30 denotes a strain gauge designed to detect the pressure.

In this way heaters of sheath type are provided in the section where thesolidfying of liquid is not desired. The arrangement of heaters can beused in association with the pressure crystallization equipment of theinvention, thereby securing the increased efficiency. Since the heatersare of a sheath type there is no difficulty in providing them. Theheaters are provided in the liquid paths alone, thereby avoiding heatingthe entire equipment, particularly the chamber where the crystallizationtakes place.

INDUSTRIAL APPLICABILITY

As evident from the foregoing description the filter structure isprotected against becoming damaged in the process of squeezing andfiltering after the crystallization has taken place, thereby separatingthe particular solidified content from the remaining liquid. Because ofthe facility and operational economy the pressure crystallizationequipment of the present invention is applicable to industrial purposes.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. Pressure crystallization equipment comprising:acylindrical high pressure vessel having an inner surface; means forestablishing a pressure of at least 500 atmospheres within said vessel;and a filter structure disposed within said vessel and being fixedagainst substantial radial and axial displacement with respect to saidvessel, said filter structure comprising a cylindrical metal meshstructure having at least two layers of mesh sintered together and areinforcement disposed between said cylindrical metal mesh structure andsaid inner surface of said vessel for backing up said cylindrical metalmesh structure, said reinforcement and said cylindrical metal meshstructure being joined together at least at opposite ends thereof, therebeing at least one liquid flow path through said reinforcement, whereina differential pressure between an inside and an outside of said filterstructure is maintained by the inner surface of said vessel.
 2. Pressurecrystallization equipment as defined in claim 1, further comprising aninsulating layer between the filter structure and the vessel. 3.Pressure crystallization equipment as defined in claim 2, wherein thefilter structure and the insulating layer are spaced from each otherwith a gap of 0.1 mm or less, and wherein the insulating layer and thevessel are spaced from each other with a gap of 0.1 mm or less. 4.Pressure crystallization equipment as defined in any of the claims 1, 2,5 or 3, further comprising a solid phase diffusion layer interfaciallyproduced between the cylindrical metal mesh layer structure and thecylindrical reinforcement.
 5. Pressure crystallization equipment asdefined in claim 1, wherein the filter structure and the vessel arespaced from each other with a gap of 0.1 mm or less.
 6. Pressurecrystallization equipment as defined in claim 1, wherein an inner wallsurface of the filter structure is shaped like a truncated conedivergent toward an open end of the vessel.
 7. Pressure crystallizationequipment as defined in claim 1, wherein the vessel comprises acylindrical body section and a bottom closure, the body section and thebottom closure being relatively shiftable to the vessel for attachingand detaching the bottom closure.
 8. Pressure crystallization equipmentas defined in claim 1, further comprising a nozzle arrangement in adischarge line communicating with a discharge path of the vessel. 9.Pressure crystallization equipment as defined in any of the claims 1 or8, further comprising a heating element of sheath type clad withelectrical insulation and disposed in liquid paths which are subjectedto high pressure.